Snapping faces: wrong orientation
Blender is snapping with the &quot;negative Z axis&quot; of the origin point.
Adjust you origin rotation and it will work.

Enable Transform Only Origin option and Face snapping
Snap the origin to a face - it'll inherit it's direction (Z+ axis)
Rotate the origin 180° along local Y axis (so it's Z-)

Snap origin and rotate it 180° along local Y axis